1. Field of the Invention
The embodiments herein relate to a transparent organic light emitting display device and a method for manufacturing the same, and more particularly, to a transparent organic light emitting display device with an auxiliary electrode and pixel/sub pixel layouts for enhancing the image quality without sacrificing the luminance and transparency of the display device.
2. Description of the Related Art
An organic light emitting diode (OLED) display device, as a self-emission display device, does not require a separate light source as a liquid crystal display (LCD). Further, the OLED display device is more power efficient and has better response speed, viewing angle and contrast ratio, making it a promising next-generation display device.
The OLED display device includes a plurality of OLED elements that can be classified into one of a top emission type, a bottom emission type and a dual emission type OLED element depending on the direction of emitted light exiting the OLED element. For example, an OLED element can be classified as a bottom emission mode OLED element if the light emitted from the OLED element passes through a transparent or a semi-transparent bottom electrode (e.g., a node) and substrate on which the OLED element was manufactured. An OLED element can be classified as a top emission type OLED element if the light emitted from the OLED element exits through a transparent or a semi-transparent top electrode (e.g., cathode). Also, an OLED element can be classified as a dual emission mode OLED element if the light emitted from the OLED element exits through both the top and bottom electrodes to emit light on both sides of the OLED element.
In an organic light emitting display device employing top emission type organic light emitting element, an electrode having a transparent characteristic or an electrode having a semi-transmissive characteristic is used as a cathode so that the light emitted from an organic emission layer exits upward through the cathode. To obtain sufficient light transmittance rate through the cathode, the cathode needs to be formed very thin. The decrease in thickness of the cathode, however, increases its electrical resistance. The increased electrical resistance, in turn, causes voltage drop in some parts of the organic light emitting display device creating non-uniform luminance throughout the screen. The voltage drop phenomenon intensifies as size of the display device increases. In this specification, the term “voltage drop” refers to the phenomenon in which a potential difference between an anode and the cathode of the organic light emitting element decreases.
To solve the voltage drop problem, an auxiliary electrode can be used in the organic light emitting display device to provide a common voltage at the location where the voltage drop is expected to occur. The auxiliary electrode, however, needs to have sufficient size and thickness to serve its purpose. The amount of space used by the auxiliary electrode in the organic light emitting display device reduces the available space for other components of the organic light emitting display device. The number of auxiliary electrodes employed in an organic light emitting display device makes it even harder to manage the space within the organic light emitting display device, which is often a critical aspect in most modern display devices. This is especially true for transparent organic light emitting display device, because placing the auxiliary electrode(s) in the pixel area reduces the size of the emissive area and/or the transmissive area, resulting in poor luminance and/or poor transparency through the display device.
Accordingly, there remains a need for a transparent organic light emitting display device with improved pixel layouts that can reduce the voltage drop problem without sacrificing the performance and the transparency of the device.